The absorption of light by certain materials can generate heat through nonradiative energy dissipation and exothermic photochemical reactions (Rosencwaig, A. Photoacoustics and Photoacoustic Spectroscopy (John Wiley & Sons, New York, 1990) In nanostructured materials, the heat generated through photothermal processes are confined within the individual nanostructures because heat transfer to neighboring nanostructures and the environment is slow. This enables unprecedented photothermal effects that cannot be observed in bulk materials, especially when a strong, pulsed light source is used (P. M. Ajayan, M. Terrones, A. de la Guardia, V. Huc, N. Grobert, B. Q. Wei, H. Lezec, G. Ramanath, T. W. Ebbesen “Nanotubes in a Flash—Ignition and Reconstruction” Science 296 705 (2002); Wang, N., Yao, B. D., Chan, Y. F. & Zhang, X. Y. “Enhanced Photothermal Effect In Si Nanowires”, Nano Lett. 3, 475-477 (2003)).
Polyaniline is a deeply colored conjugated polymer that has been extensively studied during the past twenty-five years for its electrical properties (MacDiarmid, A. G. “Polyaniline And Polypyrrole: Where Are We Headed?” Synth. Met. 84, 27-34 (1997). In powder form, undoped polyaniline is dark blue. When doped with acids it changes to a conducting form and the color changes to a deep green (Huang, W. S., Humphrey, B. D. & MacDiarmid, A. G. “Polyaniline, a Novel Conducting Polymer”, J. Chem. Soc. Faraday Trans. 82, 2385 (1986)) Since polyaniline has extremely low luminescence efficiency, it converts most of the energy absorbed from light into heat (de Albuquerque, J. E., Melo, W. L. B. & Faria, R. M. “Determination Of Physical Parameters Of Conducting Polymers By Photothermal Spectroscopies”, Rev. Sci. Instrum. 74, 306-308 (2003); De Albuquerque, J. E., Melo, W. L. B. & Faria, R. M. “Photopyroelectric Spectroscopy Of Polyaniline Films”, J. Polym. Sci., Part B: Polym. Phys. 38, 1294-1300 (2000); Toyoda, T. & Nakamura, H. “Photoacoustic-Spectroscopy Of Polyaniline Films”, Jpn. J. Appl. Phys. 34, 2907-2910 (1995).
Applicants had previously reported the formation and use of polyaniline powder and nanofibers (Huang, J. X. & Kaner, R. B. “A General Chemical Route To Polyaniline Nanofibers”, J. Am. Chem. Soc. 126, 851-855 (2004); Huang, J. X., Virji, S., Weiller, B. H. & Kaner, R. B. “Polyaniline Nanofibers: Facile Synthesis And Chemical Sensors”, J. Am. Chem. Soc. 125, 314-315 (2003).